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AST201H Entire Compilation of Lecture Notes

25 Pages
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Department
Astronomy & Astrophysics
Course Code
AST201H1
Professor
Michael Reid

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Description
AST201HDark matter versus dark Stars and Galaxies energy Dark matter has gravityand pulls things together whereas Introduction dark energy loosely does the Tues Jan 7 2014 opposite it expandsImage Hubble Extremely DeepSpace is very bigpossibly Field infinitely so In the 1960s it was believed thatthe contents of the universe was Space and Time solely comprised of stars galaxies Thurs Jan 9 2014 planets gas dustScenario Someone onboard aScientist Fritz Zwicky studied plane travelling at 900 kmh clusters in the 1930s He claims believes that a ball rolled on the that most of whats actually in the floor will go up to 10 kmh cluster cannot be seen with Someone on Earth witnessing the telescopes His colleagues thought same experiment sees something his missing mass idea was a bit elseIts travelling way faster nutty900 kmh10 kmh WhoseIn the 60s and 70s one of the first view is correct people to use radio telescopes wasEinstein says We can only measure Vera Rubin She observed motion relative to a given frame of individual galaxies and measured referencehow they moved Repeat the aforementionedNewtons Law of Gravity was experiment but replace the ball used to successfully launch probes object with light No matter how into space It also put in motion a the experiment is done all prediction the further you are from observers measure the same speed the center of the galaxy the slower of light the objects orbital speed RubinsThe speed of the ball is different in observation concluded backward different frames of reference results Given that the Law ofThe speed of light is invariant Gravity was probably correct she Tenets of Special Relativity came to the conclusion that there 1We can only measure speeds of had to be something working in objects relative to one another The these galaxies to create the laws of physics apply equally in all exception Rubin said that 90 of reference frames the universe is dark matter2 The speed of light is invariant invisible This observed fact of nature hasIn 1998 a new module was bizarre consequences proposed 683 of the universe isScenario Lets look at motion on a dark energy 268 is dark matter train from the perspective of two and 49 is luminous matter different observers Person on the 975 of the universe seems to be train says the ball he tossed completely missing upwards went up 1 m and cameAST201H 1 down 1 m in 1 s for a speed of 21 ly away from the Earth there is ms nothing our solar system is muchPerson on the tracks observing the smaller than 1 ly scene says the ball went up 2 m andA person on Earth who sees you came down 2 m in 1 s for a speed travel 25 light years at 0999 c they of 4 mswould think your trip takes a littleBecause two observers moving more than 25 years Heres a tip to relative to one another must agree remember when thinking about it about the speed of light they must Moving clocks run slow disagree about the time betweenYOU in a spaceship measure the events Time literally flows at distance between Earth and Vega as only 1 light year Thus for you the different rates for any two trip to Vega takes only about one people in motion relative to yearone anotherRandom fact If you travelled to theThis is called time dilation center of our galaxy and back atObservers in motion relative to one 9999999 of the speed of light another also disagree about their you would age about 8 days but lengths This is called length Earth would age about 50 000 contraction years The Twin Paradox Imagine RelativityGravity you get in a spaceship and travel to Thurs Jan 16 2014 the star Vega at 999 of the speedAnnouncements Term project of light The distance between the posted on portal draft due in two objects is approx 25 light tutorials March 4 video and audio years A light year is the distance clips max 2 mins light travels in one year Although it sounds like a lot of time it is notGravity Is extremely weak but it Think of it like a highwaydrivinghas infinite range Its functions is minuteto make masses attract one1 ly95 trillion km You dont another More mass means more have to memorize this for a test gravityClicker Question Imagine a Continuing Discussion About universe which is empty except for Relativity you and a baseball You throw the Tues Jan 14 2014 baseball If we ignore gravity whatRecall Time literally flows at will ultimately happen to the different rates for any two people baseball It will keep moving in motion relative to one another forever at a constant speed If a clock is moving relative to Newtons First Law you you will perceive the time Objects move with constant speed and on that clock to be moving direction unless acted upon by a force slowerAcceleration Is a change in speed caused by a forceAST201H 2
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